Disc drives are used for data storage in modem electronic products ranging from digital cameras to computers and network systems. Typically, a disc drive includes a mechanical portion, or head disc assembly, and electronics in the form of a printed circuit board assembly mounted to an outer surface of the head disc assembly. The printed circuit board assembly controls functions of the head disc assembly and provides a communication interface between the disc drive and a host being serviced by the disc drive.
Typically, the head-disc assembly has a disc with a recording surface rotated at a constant speed by a spindle motor assembly and an actuator assembly positionably controlled by a closed loop servo system. The actuator assembly supports a read/write head that writes data to and reads data from the recording surface. Disc drives using magneto resistive read/write heads typically use an inductive element, or writer, to write data to information tracks of the recording surface and a magneto resistive element, or reader, to read data from the information tracks during drive operations.
The disc drive market continues to place pressure on the industry for disc drives with increased capacity at a lower cost per megabyte and higher rates of data throughput between the disc drive and the host. High performance disc drives achieve areal bit densities in the range of several gigabits per square centimeter (Gbits/cm2). Higher recording densities can be achieved by increasing the number of bits per centimeter stored along each information track, and/or by increasing the number of tracks per centimeter written across each recording surface. Capacity increases gained by increasing the number of tracks per centimeter on each recording surface generally require improvements in servo control systems, which enable the read/write heads to be more precisely positioned relative to the information tracks. Capacity increases gained through increasing the bits per centimeter stored on each track generally require improvements in the read/write channel electronics to enable data to be written to and subsequently read from the recording surface at a correspondingly higher frequency, and typically foster a need for improvements in the interface channel electronics for improved bit transfer rates.
Under a typical queued command environment architecture for a host interface channel of a disc drive, requested read data that must be retrieved from the media requires synchronization between the host interface channel of the disc drive and the drive interface channel of the host in order to steam the read data almost immediately to the drive interface channel of the host. A problem with this method of handling data read requests is that the drive interface channel of the host is connected with the host interface channel of the disc drive exclusively while the data is recovered from the media.
For any media access, the access time is governed primarily by the seek time and by the rotational latency. Since seek times are generally in the millisecond time frame, the disc drive cannot transmit or receive other data while the drive interface channel of the host is connected with the host interface channel of the disc drive. In a queued command environment, there is no host transfer activity permitted during this access time and this can result in a significant decrease in overall data transfer rate. This problem also exists for non-WCE (Write Cache Enabled) writes since the final status transfer of the host interface channel of the disc drive maintains control over the drive interface channel of the host until the disc write operation completes.
As such, challenges remain and a need persists for improvements in data throughput between the disc drive and the host. It is to this and other features and advantages set forth herein that embodiments of the present invention are directed.